There are a number of different methods for cooling a flowing stream of air. Indirect evaporative cooling invented in the mid-seventies (see, for example, Schlom, et al., U.S. Pat. Nos. 4,023,949 and 6,385,987) uses the latent heat of the evaporation of water to remove heat from the air.
Direct evaporative coolers on the other hand, also known as swamp coolers, cool the air by passing the air through wet pads by which the evaporative absorption of the latent heat of evaporation by the water directly cools the air. Since the water vapor evaporates directly into the air, the air ends up with a high moisture content.
With direct refrigeration, incoming hot air passes through a heat exchanger where a refrigerant composition, such as Freon, absorbs heat from the air and evaporates. The latent heat of evaporation of the refrigerant acts on the air through a heat exchanger to cool the air. To recycle the refrigerant, additional energy is used to compress and condense the refrigerant vapor back to a liquid, which can then be returned to the intake of the heat exchanger and evaporated again in a regular cycle.
There are two notable differences between indirect evaporative cooling and direct refrigeration. The first is that indirect evaporation evaporates water instead of Freon in the heat exchanger. The second is that the water vapour in indirect evaporative cooling is not recaptured and condensed back to the liquid state as is Freon in direct refrigeration.
Evaporative cooling is especially well suited for climates where the air is hot, humidity is low and where the energy demands of refrigerative cooling are impractical. Evaporative air conditioning is popular and well suited to desert and desert-like regions.
In dry, arid climates, the installation and operating cost of an evaporative cooler can be much lower than refrigerative air conditioning, often by 80% or so. However, evaporative cooling and vapor-compression air conditioning are sometimes used in combination to yield optimal cooling results. Some evaporative coolers may also serve as humidifiers in the heating season.
In locations with moderate humidity, there are many cost-effective uses for evaporative cooling. For example, industrial plants, commercial kitchens, laundries, dry cleaners, greenhouses, spot cooling (loading docks, warehouses, factories, construction sites, athletic events, workshops, garages, and kennels) and confinement farming (poultry ranches, hog, and dairy) all often employ evaporative cooling. In highly humid climates, evaporative cooling may have little thermal comfort benefit beyond the increased ventilation and air movement it provides.
Residential or commercial building air conditioners face special challenges when operated in environments having airborne sand, salt, and dust. Narrow flow channels for liquids and/or air for direct or indirect heat exchange in conventional air cooling units can quickly become clogged and fouled with airborne debris which can materially affect the efficiency and operation of the cooling unit.
Conventional desert coolers uses large water tank and one or more submersible pumps inside tank pumping and dripping water over Evaporative cooling media honeycomb cellulose cells or hass type. Some of the problems of conventional evaporative air coolers are as follows:                It is not possible for such units to supply air equal to outdoor air wet bulb temperature as it need to be at 100% saturation which may not be comfortable for human also may not be suitable for most applications.        An unstable supply air temperature due to fluctuations of the tank water temperature.        Supply air temperature depend on the water temperature in the tank, since water tank is the base and external body of the unit which increase water temperature in tank higher than the outdoor wet bulb temperature.        Salt problem causing fast media clogging, also corrosion of body and internal parts like fan, and pump continues failure.        Conventional desert coolers are continuously accumulating unhealthy dirty dust with high dirt and salt concentration water inside tank.        To directly cool supply water or tank water to a temperature less than outdoor wet bulb require high cooling capacities.        